Applicant's U.S. Pat. No. 5,052,230 discloses an ultrasonic volumetric flowmeter comprising
two ultrasonic transducers operated as transmitter or receiver which are disposed oppositely to each other along a pipe carrying the fluid to be measured and are separated by a given distance in the direction of the axis of the pipe, and PA1 driver/evaluation electronics which PA1 two ultrasonic transducers operated as transmitter or receiver which are disposed oppositely to each other along a pipe carrying the fluid to be measured and are separated by a given distance in the direction of the axis of the pipe, PA1 a first additional transducer, PA1 a second additional transducer, PA1 driver/evaluation electronics which PA1 additional electronics PA1 at least two ultrasonic transducers operated as transmitter or receiver which are disposed on the outside surface of a pipe carrying the fluid to be measured and are separated by a given distance in a direction parallel to the axis of the pipe, and PA1 driver/evaluation electronics PA1 a first pair of ultrasonic transducers PA1 a second pair of ultrasonic transducers which are operated simultaneously as transmitting transducers or receiving transducers, and which are disposed on the outside surface of the pipe and are separated by a given distance in a direction parallel to the axis of the pipe, such that the angle between the direction of the ultrasound generated by them and the axis of the pipe is less than or equal to 90.degree.; and PA1 driver/evaluation electronics PA1 which measure, in a direction perpendicular to the axis of the pipe, the orthogonal travel time of the ultrasonic signal in the wall of the pipe and the orthogonal travel time of the ultrasonic signal propagating through the fluid and reflected at the inside surface of the pipe opposite the additional ultrasonic transducer, PA1 which are supplied with a circumference signal proportional to the outer circumference of the pipe and with a sound-velocity signal proportional to the velocity of sound in the material of the pipe, and PA1 which determine the wall thickness of the pipe and the velocity of sound in the fluid from the two orthogonal travel times, the circumference signal, and the sound-velocity signal.
feed the two ultrasonic transducers successively with a sine-wave burst, measure the travel times of ultrasonic signals propagating from one ultrasonic transducer through the fluid to the other ultrasonic transducer in the downstream and upstream directions, and determine volumetric flow rate therefrom. PA2 feed the two ultrasonic transducers successively with a sine-wave burst, measure the travel times of ultrasonic signals propagating from one ultrasonic transducer through the fluid to the other ultrasonic transducer in the downstream and upstream directions, and determine volumetric flow rate therefrom, and PA2 which measure, in a direction perpendicular to the axis of the pipe, the orthogonal travel time of the ultrasonic signal in the wall of the pipe by means of the first additional transducer and the orthogonal travel time of the ultrasonic signal propagating through the fluid and reflected at the inside surface of the pipe opposite the second additional transducer by means of this second additional transducer. PA2 which supply the at least two ultrasonic transducers simultaneously with a pulse burst and, using correlation techniques, measure the time difference between signals reflected at foreign particles in the fluid and received in the intervals between the pulse bursts by the at least two ultrasonic transducers, and determine volumetric flow rate therefrom. PA2 one of which is operated as a transmitting transducer and the other as a receiving transducer or vice versa, or PA2 which are both operated as transmitting transducers and subsequently as receiving transducers for short times, and PA2 which are disposed on the outside surface of a pipe carrying the fluid to be measured and are separated by a given distance in a direction parallel to the axis of the pipe, such that the angle between the direction of the ultrasound generated by them and the axis of the pipe is different from 90.degree.; PA2 which supply one or both ultrasonic transducers of the first pair with a pulse burst, measure the travel times of ultrasonic signals propagating between said ultrasonic transducers through the fluid in the downstream and upstream directions and reflected at the inside surface of the pipe opposite said ultrasonic transducers, and determine volumetric flow rate therefrom (=travel-time electronics), or PA2 which supply the ultrasonic transducers of the second pair simultaneously with the pulse burst and, using correlation techniques, measure the time difference between signals reflected at foreign particles in the fluid and received in the intervals between the pulse bursts by said ultrasonic transducers, and determine volumetric flow rate therefrom (=correlation electronics), and PA2 which include threshold changeover electronics with a threshold switch
WO-A-88/08516 discloses a clamp-on ultrasonic volumetric flowmeter comprising
U.S. Pat. No. 4,484,478, U.S. Pat. No. 4,598,593, and EP-A-446 023 each disclose a clamp-on ultrasonic volumetric flowmeter comprising
The ultrasonic volumetric flowmeter disclosed in the above-mentioned U.S. Pat. No. 5,052,230 and the clamp-on ultrasonic volumetric flowmeter disclosed in the above-mentioned WO-A-88/08516 are intended only for fluids containing no foreign particles, and become inoperative when the foreign-particle content increases, since the ultrasound is scattered and/or absorbed in the fluid so strongly that it does not reach the receiver in sufficient strength.
The clamp-on ultrasonic volumetric flowmeters disclosed in the above U.S. Pat. No. 4,484,478, U.S. Pat. No. 4,598,593, and EP-A-446 023 are intended only for fluids containing foreign particles, but will fail if foreign-particle-free fluids are to be measured.
In practice, however, it cannot be ruled out that fluids which should be free from foreign particles contain foreign particles after all, which then interfere with or even prevent the measurement, and that fluids supposed to contain foreign particles are, by way of exception, free from foreign particles, which also interferes or even prevents the measurement.